With training camp just days away, we’re going to ask a question a day about the upcoming Nets season.

Can the Nets finish this season with a top-10 defense?

If you want to be a championship-caliber team in the NBA, there is one near universal truth: You have to be able to play defense.

Take a look at last season. The now two-time defending champion Miami Heat finished the regular season with the league’s best offense, but also had the seventh-best defense. The Spurs finished the regular season with the third-best defense, behind the Pacers and Grizzlies.

All told, the only two teams that made even the second round of the playoffs that finished outside the top 10 in defense were the Warriors, who finished 13th, and the Knicks, who finished tied for 17th.

So it’s clear the Nets — who finished last season tied with the Knicks in defensive rating, also known as points allowed per 100 possessions (statistical rankings courtesy of NBA.com) — are going to have to improve their defense significantly if they want to make a serious run at the top of the Eastern Conference, let alone an NBA title.

Can they do that? The answer may lie in just how much life is left in Kevin Garnett’s legs. Garnett is simply one of the best defensive big men in the history of the NBA. Even last season, at 37, Garnett had a profound impact on the Celtics’ defense when he was on the floor.

In the minutes Garnett was on the floor for Boston (which finished sixth overall in defense), the Celtics allowed 96.2 points per 100 possessions — a number that would have bested Indiana’s league-leading mark of 96.6 points per game. But when Garnett wasn’t on the floor, the Celtics’ defense dropped off dramatically to 104.6 points per 100 possessions, which would have ranked 21st over the course of the full season.

So, assuming health, the addition of Garnett, along with defensive stopper Andrei Kirilenko on the wing, should go a long way towards helping the Nets improve their defense. They also hope Lawrence Frank, who has rejoined the Nets as Jason Kidd’s defensive coordinator, will help as well.

But the Nets are going to need improvement from a lot of returning players. Reggie Evans was the best of any Net who played significant minutes in terms of defensive rating, but the Nets still allowed 101.9 points per 100 possessions when he was on the floor. While the Nets were two points better when Brook Lopez on the floor (102.6 compared to 104.6), they were only half a point better with Joe Johnson playing and a full five points worse with Deron Williams on the floor (105.0 to 100.0).

It’s clear the Nets have work to do in order to go from a tie for 17th into the top 10 in team defense. But improving on that side of the ball is a key to achieving their lofty goals this season.